Hydrocarbon conversion process



April 6, 1948- s. P. ROBINSON HYDROCRBON CONVERSION PROCESS Filed July16, 1946 IN V EN TOR. SAM R ROBINSON @fr ATTO-RNEYS I Patented Apr. 6,1948 p' vsinn r.

v Delaware Robinson, om, minor to Petroleum Company, a corporation or- 4Application .my 1e, 194e, serial No. 683,839

This invention relates to the conversion of hydrocarbons. In oneembodiment it relates to the conversion of low-boilingv paraiilnhydrocarbonsl or of low-boiling oleiin hydrocarbons, other than adesired unsaturated hydrocarbon, to a lowboiling unsaturatedhydrocarbon, and the recovery of the resulting unsaturated hydrocarbonin a highly concentrated form.y Anotherembodiment ofthe inventionrelates to the production of ethylene by conversion of normally gaseoushydrocarbons heavier than methane.

The conversion of hydrocarbons to other,.1ess saturated hydrocarbons oflower molecular weight can -be readily effected at temperatures above'.

about 1000 F. .Such reactions are endothermic, so that it is necessaryto supply large quantities of heat, at these high temperatures, in orderto town. (c1. zoo-ssa) sion, and a relatively `complex combination ofcompressora'separators, coolers, condensersl, fracdividualdesiredunsaturated hydrocarbon prod;4 uct in relatively pure form.. Forsuccessful' operation ,such equipment must be maintained loaded withhydrocarbon material and the temperature, pressure. and composition ofthe hydrocarbon mixtures present in any given portion or part of suchcombination equipment should remain relatively constant. I have now alsoobtain an extensive conversion, per pass, od! the y charge stock.However, the resulting unsaturated hydrocarbons, such as oleilns,dioleiins, acetylenes, etc., are quite reactive at these same hightemperatures, and readily take part in polymerization or condensationreactions which are found that such equipment can be potected byproviding for prompt and positive discharge of the reaction emuents fromthe system in the event adequate coolingor quenching oi these eiiluents`fail and, at .the same' time, providing for cutting oi! the supply ofheat to the conversion zone.

It is an object of this invention to effect a conversion of hydrocarbonsat a high temperature.

Another object of this inventionv is to convert 1 other hydrocarbons toethylene.

highly exothermic. As a result, in order to convert a given hydrocarbonmaterial to less saturated hydrocarbons of lower molecular weight notonly must the hydrocarbon material be heated to 'a high temperature andhave considerable quantities of heat supplied `to it at a hightemperature level, but the reaction conditions must be closelycontrolled. This control must be. effective not only ,to prevent loss ofdesired products by secondary reactions but also to prevent a conversionprocess from getting out of control .as a result of extensive and seli.'accelerating exothermic reactions of such unsaturated hydrocarbons. Ihave now found that a continuous conversion process of this nature maybe readily lcontrolled by a rapid cooling, or quenching, of thereaction. Reaction `times for the desired endothermic reaction aredependent upon the temperature of the conversion and vary, more or lessinversely with the temperature, from a few seconds (less than a minute)to as low as about 0.01 second. At temperatures in the region of, andbelow, 1000 F.

the undesired exothermic reactions do not take Still another object ofthis invention is .to convert hydrocarbons at a high temperature to low-,boiling unsaturated hydrocarbons with a minil mum formation ofhigh-boiling hydrocarbons.l`

A further object or my invention is to provide44 apparatus for emergencyhandling of hydrocarl bon conversion equipment.

Further objects and advantages of my inven-r tion will become apparent,to one skilled in the art, from the accompanying disclosure anddistroduced through line 9, and of a recycle stream passed through line55. It is often preferred that this material be substantially free fromsulfur compounds, such as hydrogen sulfide and mercaptans, and when sodesired a :sulfur-containing Y charge may be treated to reduce itssulfur contional distillation columns,- and all'usually assol ciatedequipment, is necessary to isolate an intent. This charge stock, at apressure not greater than about 40 pounds per square inch absolute, ispassed through an expansion valve or orifice ii to preheating coil I2and cracking or dehydrogenating coils I3 and I4, which are situated infurnace i5. In coils It and I4 the charge is heated to a temperature ofabout 1350 to about i650 F. for a time suicient to give an optimum yieldof ethylene. This will generally be about 1.5 to about 0.15 second. Inactual plant operation, a furnace i5 will have a plurality of preheatingand cracking coils operating in parallel and by means of an expansionvalve or expansion orice il at the inlet to each set of coils, the flown;v

through the sets of coils will be more or less uniform. To thehydrocarbon stream, prior to its introduction to the reaction zone,steamV is added through line I6. Enough steam is used to passivatecatalytic metal and depress coke formation. In some instances about 0.1to about 0.5%v

by weight of sulfur will have a similar effect. However, when about 0.2to 0.5 mol of steamv per mol of hydrocarbon is used, the effect of thedecreased partial pressure of'hydrocarbon re-v actants is beneficial,and leads to optimum ethylene production, and serves to minimizepolymerizing of oleflns produced. It is preferred that, in the crackingcoils I3 and I4, tubes of a small diameter be used, receivingdirect-radiant heatl and with the diameter of the tubes and the flow ofreactants through the tubes so correlated that a lower than usual rate'of heat transfer through the tube walls takes place. This results inhaving more uniform gas temperatures throughout the cross-sectional areaof the cracking tube and increases the ratio of heat transfer area percubic foot of gas handled.

Eiiluents of cracking coil I4 are passed through line I1 to tarseparator 20. Immediately upon the exit of the gases from cracking coilI4, water is injected through line I8 to cool the gases as rapidly aspossible, to a temperature below about 1000 F. .Unless this is done,beneficial results from careful design of the cracking coils and controlof flow rates with heat transfer rates to produce optimum ethyleneproduction will be lost, because ethylene is highly reactive and readilypolymerizes at the reaction temperatures. The amount of water introducedthrough line I8 is controlled by valve I9, which is responsive to thetemperature in line I1 at a point which is down stream from the point cfwater injection. Ad-

a ditional quantities of water are added through liney 22to bring thetemperature of the gases to about250 to about 350 F. As a result, someof the heaviest tars produced during the cracking reaction are condensedand separate from th'e uncondensed gaseous material. Such tars can bedischarged from the process through line 23.

Uncondensed gases pass from tar separator 20 through line 25 to quenchtower 26, wherein they are intimately contacted with a spray of watervintroduced through line 30. The temperature at the top of tower 26 ismaintained at about 120 to` about 160 F., resulting liquid oils aredischarged through line 2'I. Water at a temperature of about 165 to 265F, is removed through line Y28, cooled in cooler and condenser 29, and

recirculated to the process either through line 30 tower 26 through line35, and passed through cooler 36 to a rst separator 31. The temperatureof these gases is maintained at between about 120 and 160 F., by controlof valve 33 in .water line 30 in response to the temperature of thedischarged gases. From separator t1 condensed water is removed throughline B5 and light oils are passed back to the water quench tower 26through line 46. The gases in this rst separator are'at a temperature ofabout to 130 F. and under a pressure which is slightly above atmosphericpressure, but not greater` than about 30 pounds per square inch'absoluta', Gases are removed through line 41, and passed to separatingmeans'i.' Separating means 50 comprises a combination of suitablecompressors, coolers, condensers, separators, ,driers,A fractionaldistillation columns, etc., and usual associated equipment, forseparating desired hydrocarbon fractions; In this particular vinstancean ethyleney fraction, in which ethylene is to 95%, or more, of thetotal fraction, is recovered through line 5I. A fraction comprising freehydrogen is recovered through line 52, a fraction comprising methane isrecovered through line 53, and undesired heavy hydrocarbons aredischarged through line 54. A Ca-Cs fraction is recovered through line55, and maybe recycled to the conversion step or discharged, entirely orin part, through line 56. A highly efficient combination of equipmentfor effecting the separation of such fractions is more fully disclosedand discussed by K. H. Hachmuth in his application Serial No. 683,904,filed July 16, 1946.

At the point 2| in line 25 is a thermocouple or other temperatureindicating means, which actuates means to open valve 4| in line 40 andmeans to close valve 43 in fuel supply line 42. Whenever for any reasonthe temperature of the gases passing through line 25 rises sufficientlyabove the desired normal range of 250 to 350 F. that a temperature ofincipient exothermic reaction is approached (generally about 1000 F.)this combination of apparatus immediately discharges the gas passingfrom the top of quench tower 26 andV As will be appreciated by oneskilled in the art, the drawing is entirely diagrammatical, and inactual operation, various additional pieces of conventional equipment,such as pumps, control valves', temperature indicating, recording, andcontrol devices, heaters forreboilers, coolers, heat exchangers,insulation for transfer lines and fractional distillation columns,accumulators and the like, containing materials at subatmospherictemperatures, will obviously be included and can be readily incorporatedin any specific case. The temperatures used in the various steps will beclosely dependent upon the pressure used, and both will be somewhatdependent upon the compositions of the materials being treated.

My invention will be further illustrated by the following example. Inconnection withl this example, reference is made back to various piecesyactuating the operation of motor valves at 4I and the accompanyingtable. To this is added a recycle stream trom line, also shown in theaccompanying table, and steam tol give a total furnace feed passingthrough expansion orince l I as shown in the table. Compositions in thetable suiiiclent to produce an optimum'yield of cth--4 5 their passagefrom said conversion zone in an are'inmol percent. amount such as tocool said eiliuents to a temu W" 9 om n Line 1v Line s2 Line se 'Line s1Line tu 12:08 Tm Furnace E Methane Ethylene (Jr-0a Feed F.0d EiliuentFraction Fraction Product Recycle B4- 16.0 01.8 1.7 on a7 4.a 20.0 00.005.3 2.1 Co a 0.1 0.4 c. i as 4.1 24.8 0.4 2.0 95.0 4.7 c- 14.4 10.3 0.00.0 0.4v 2.5 34.1 C- 29.3 21.0 5.4 41.4 Gf- 44.1 33.1 1.1 as C) il. 0. 10. 5 n. s. 1.5 a1 C411. 1 o 0.a 0.2 1.4 ons 2.1 .0.1 Tara... 0.3 m0 25.010.5

from 100.0 100.0 100.0 100.0 100.0 100.0 100.0

mixture is subjected to cracking at a maxinum temperature of about 1470F. under an exit pressure of about pounds per square inch ab- 25 trolledvalve I9, to the stream immediately upon 30 its exit from the crackingcoil, to bring the temperature down below 1000 F. Additional water isthen added through line 22 to bring the stream temperature to about 300F. A small amount of tar is removed through line 2l, and the gase- 35ous eiuent is passed through line 25 to water quench tower 2 6. A streamof water, introduced through at about 100 F., cools the gases passingthrough line to about 140 F. When an o abnormal interruption in servicescauses the temperature of the gas passingnpoint 2| to rise from itsnormal temperature ci! about 300 F. to about .1000 F., valve 4Iimmediately opens to discharge the gas passing from quench tower26, andvalve I3 immediately causes the nre in furnace I5 to be killed.

Cooler 36 cools the gas to -about 100 F. and condenses most of theremaining water, which i-s discharged through line 45. The remaininggaseous materialis passed through yline 41 to separatingmeans 50 whereinit is compressed to a pressure of about 600 pounds per square inchabsolute, cooled, and subjected to a series of fractional distillationsteps. The hydrogen discharged through line 62 has the composition shownin the table, and the methane fraction discharged through line 53 hasthe composition shown. The resulting gaseous ethylene stream, removed asa product of the process through line 5I, is substantially pure, havingthe composition n shown in the table.

It will be appreciated that various modications of my invention can bepracticed, by one skilled in the art, without departing from the scopeor spirit of the disclosure or claims.

I claim:

1. An improved process for the production fof ethylene, which comprisespassing a reactant stream comprising primarily ethane, propylene andpropane together with steam through a long, narrow, extern-ally heatedconversion zone, subjecting said stream in said conversion zone to atemperature between about 1350 and about 1650 F. under 9, pressurebetween about 15 and about pounds per square inch absolute for a timeeous hydrocarbon eilluents oi said scrubbing zone to separating meansand recovering from said separating means a hydrocarbon fractioncomprising ethylene so produced as a product of the process, andsimultaneously discharging from the' process said gaseous hydrocarboneilluents of said scrubbing zone and cutting on the supply or heat tosaid conversion zone whenever the temperature of the stream of saidgaseous mixture entering said scrubbing'zone reaches about 1000 F.

2. An improved process for conversion of propane tooptimum yields oi' C:and lighter unsaturated hydrocarbons with minimum concomitant yields ofhigher-boiling hydrocarbons, which comprises continuously passing a.normally gaseous hydrocarbon. material comprising propane through along, narrow conversion zone, heated by combustion of a fuel,maintaining the contents oi said conversion zone at an elevatedconversion 5o temperature above about 1150 F. and a low pressure for atime such as to produce an optimum yield oi' Ca and lighter unsaturatedhydrocarbons together with a minimum of heavier hydrocarbons,continuously introducing water into the stream of reaction productsimmediately after their passage from said conversion zone in an amountsuch as to cool said eiiuents to a temperature below about 1000 F.,subsequently introducing additional water in an amount suincient to coolsaid reaction eilluents to about 300 zone to separating means, andcompletely shutting oft` the aforesaid fuel and simultaneously divertingto discharge from the process the gaseous effluent normally passing fromsaid scrubbing zone to said separating means whenever the temperature ofsaid gaseous material entering said scrubbing zone reaches about 1000 F.

3. An improved process for the conversion of a hydrocarbon to anunsaturated hydrocarbon of lower molecular weight, which comprisespassing a. stream of a hydrocarbon material heavier than methane througha heated conversion zone. sub- .casacca molecular weight, immediatelyand rapidly cool-r ing effluents of said conversion zone to atemperature below that at which unsaturated hydrocarbon products of saidconversion riti `nndergo secondary reactions to produce hydrocarbons ofhigher molecular weight, passing cooled hydrocarbon eiiiuents toseparating means and recovering therefrom a hydrocarbon fractioncomprising an unsaturated hydrocarbon oi low molecular weight soproduced as a product or the process, and simultaneously dischargingfrom the process the normal charge to said separating means and cuttingon the supply of heat to said conversion zone whenever effluents of saidconversion zone are not cooled to a temperature suiciently low toinhibit secondary reactions of said unsaturated hydrocarbon products oflow molecular weight.

4. Apparatus forthe conversion of hydrocarbons to unsaturatedhydrocarbons of lower molecular weight which` comprises, in combination,a. conversion zone, a, source of heat for said conf version zone,separating means for recovering a 'connecting said-conversion zone andsaid separatv"ing meansgfmeans for cooling eiiiuents of. said yAconversioncaone :passingthrough said conduit@1` `vrneans'prior.toftheirintroduction into said separating means,`normallyclosed emergency dis-` charge means for discharging the contentsof saidconduit means downstream from said cooling means@ temperatureresponsive device in said conduitrneans downstreamv from said coolingmeans and upstream from said separating means and said discharge means,and means responsive Y to an elevated temperature indicated by saidtemperature responsive device for opening-said disdesired product ofsaid conversion, conduit means l charge means and simultaneously cuttingoff said 'i source of heat.

. SAM R ROBINSON.

REFERENCES CITED The following references kare of record in the-2,263,557 Greenewalt Nov. 25, 1941

